The Old Order Amish of Lancaster County, Pennsylvania, initially numbered in the hundreds, and are now a population of over 30,000. This population is a well-defined, genetically homogeneous Caucasian population with very large sibships, a high degree of consanguinity, and well-documented genealogies. The goal of this study is to recruit and phenotypically characterize large multiplex pedigrees with noninsulin-dependent diabetes mellitus (NIDDM) for a genome-wide search for susceptibility genes for this heterogeneous and polygenic disorder.